Center channel positioning apparatus

ABSTRACT

A center channel positioning apparatus is provided, which does not cause strange feeling in sound quality even at a position apart from an original listener position. 
     A sound signal processing unit ( 40 ) changes a phase of at least one of a left sound signal for center channel positioning (CL) and a right sound signal for center channel positioning (CR), based on a processing coefficient, and causes a left speaker ( 46 ) and a right speaker ( 52 ) to output sound based on a center channel sound signal (C). 
     The processing coefficient is calculated based on the difference in level between both ears in the case where the left sound signal for center channel positioning (CL) for the left speaker ( 46 ), and the right sound signal for center channel positioning (CR) for the right speaker ( 52 ) are reproduced simultaneously.

TECHNICAL FIELD

The present invention relates to a center channel positioning apparatus.In particular, the present invention relates to a center channelpositioning apparatus which causes sound based on a center channel soundsignal to be outputted from a left speaker and a right speaker.

BACKGROUND ART

Conventionally, in a surround system such as a 5.1-channel system, threespeakers of a left speaker, a right speaker, and a center speaker arelocated in front of a listener, and it is desirable that the centerspeaker is located between the left speaker and the right speaker.However, since a display apparatus such as a television set is locatedbetween a left speaker and a right speaker, it is difficult that acenter speaker is located between a left speaker and a right speaker.

Therefore, a surround system is proposed, in which a center speaker isomitted, and a center channel positioning based on a center channelsound signal is virtually formed by a left speaker and a right speaker.

In such a surround system mentioned above, a case will be mentioned, inwhich a center speaker is located in front of a listener position, and aleft speaker is located with an angle of 30° in the left direction fromthe listener position, and a right speaker is located with an angle of30° in the right direction from the listener position. A frequencycharacteristic in the case where a center channel sound signal isreproduced by left and right speakers is compared with a frequencycharacteristic in the case where the center channel sound signal isactually reproduced by a center speaker. In the case where a centerchannel sound signal is reproduced by left and right speakers, there isa problem that a gain is lowered by approximately 10 dB at a frequencyband of approximately 1 to 4 kHz.

An apparatus for solving the above problem is shown, for example, inPatent Document No. 1.

-   Patent Document No. 1: Japanese Patent Laid-open No. 2004-266604

In a reproducing apparatus disclosed in Patent Document No. 1 mentionedabove, after a center channel sound signal is processed by an equalizerin such a way that its frequency characteristic is corrected, theresultant signal is reproduced by left and right speakers. Acharacteristic of the equalizer is one which causes a frequencycharacteristic of a head transfer function in the case where a centerchannel sound signal is reproduced by left and right speakers to beequal to a frequency characteristic of a head transfer function in thecase where the center channel sound signal is actually reproduced by acenter speaker.

Concretely, at a frequency band of approximately 1 to 4 kHz, a level offrequency characteristic in the case where a center channel sound signalis reproduced by left and right speakers becomes lower than a level offrequency characteristic in the case where the center channel soundsignal is actually reproduced by a center speaker, by approximately 10dB. Therefore, an equalizer has a characteristic which causes a gain tobe raised by approximately 10 dB at a frequency band of approximately 1to 4 kHz.

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

In a reproducing apparatus disclosed in Patent Document No. 1 mentionedabove, a correction characteristic of an equalizer is set on theassumption that in the case where a left speaker is located with anangle of 30° in the left direction from a listener position, and a rightspeaker is located with an angle of 30° in the right direction from thelistener position, a center channel sound signal is heard at thelistener position.

Therefore, in the case where a center channel sound signal is heard at aposition apart from an original listener position, only a component of afrequency band of approximately 1 to 4 kHz for which a gain has beenraised by approximately 10 dB, of components of a center channel soundsignal, is heard. As a result, strange feeling in sound quality iscaused to a listener.

The present invention has been achieved in view of the above problem, itis an example of an object of the invention to provide a center channelpositioning apparatus which does not cause strange feeling in soundquality even at a position apart from an original listener position.

Means for Solving the Problem

In order to solve the above problem, the invention according to claim 1relates to a center channel positioning apparatus, comprising:

-   -   a sound signal outputting unit which outputs a left sound        signal, aright sound signal, and a center channel sound signal,    -   a sound signal processing unit which produces a left sound        signal for center channel positioning, and a right sound signal        for center channel positioning, based on the center channel        sound signal,    -   a left sound signal combining unit which combines the left sound        signal with the left sound signal for center channel positioning        to output a left combined sound signal to be supplied to a left        speaker, and    -   a right sound signal combining unit which combines the right        sound signal with the right sound signal for center channel        positioning to output a right combined sound signal to be        supplied to a right speaker,    -   wherein the sound signal processing unit changes a phase of at        least one of the left sound signal for center channel        positioning and the right sound signal for center channel        positioning, based on a processing coefficient, and    -   the processing coefficient is calculated based on the difference        in level between both ears in the case where the left sound        signal for center channel positioning and the right sound signal        for center channel positioning are reproduced simultaneously,        and the sum of power at both ears of the left sound signal for        center channel positioning and the right sound signal for center        channel positioning.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block circuit diagram of a center channel positioningapparatus according to an embodiment of the invention.

FIG. 2 is a circuit diagram showing a structure of the inside of a soundsignal processing unit shown in FIG. 1.

FIG. 3 is a circuit diagram showing an input of a sound signalprocessing unit shown in FIG. 1.

FIG. 4 is a view of arrangement showing the relationship in positionbetween a listener, and a left speaker and a right speaker.

FIG. 5 is a view of graph showing an amount of delay for each band in anall-pass filter.

FIG. 6 is a view of arrangement showing the relationship in positionbetween a listener, and a left speaker and a right speaker, in the casewhere a subjective evaluation experiment is conducted.

FIG. 7 is a view of graph showing a result of a subjective evaluation ina center channel positioning.

FIG. 8 is a view of graph showing the difference in level between bothears.

FIG. 9 is a view of graph showing the attenuation of sum of power atboth ears.

FIG. 10 is a view of graph showing a degree of center positioning.

DESCRIPTION OF REFERENCE NUMERALS

-   10: sound source-   12: AV amplifier device-   14: speaker unit-   16: decoder-   36: left sound signal combining unit-   38: right sound signal combining unit-   40: sound signal processing unit-   46: left speaker-   48: right speaker-   56: all-pass filter-   C: center channel sound signal-   CL: left sound signal for center channel positioning-   CR: right sound signal for center channel positioning

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIG. 1 to FIG. 10, a best mode for carrying out theinvention will be described.

In FIG. 1, a block circuit diagram of a center channel positioningapparatus according to an embodiment of the invention is shown.

In FIG. 1, a digital stream signal 100 from a sound source 10 such as aDVD player is supplied to an AV amplifier device 12, and a speaker unit14 is connected to the AV amplifier device 12. Hereinafter, a structureof the AV amplifier device 12 is described.

The AV amplifier device 12 includes a decoder 16. The digital streamsignal 100 is supplied to the decoder 16, and the decoder 16 decodes asignal of 5.1 ch. Surround signals SL, SR, and SW from the decoder 16are supplied through DA conversion units 18, 20, and 22 to amplifierunits 24, 26, and 28, respectively. Outputs from the amplifier units 24,26, and 28 are supplied to surround speakers 30, 32, and 34 in thespeaker unit 14.

The decoder 16 outputs a left sound signal L, aright sound R, and acenter channel sound signal C. The left sound signal L, and the rightsound R are supplied to a left sound signal combining unit 36, and aright sound signal combining unit 38, respectively. The center channelsound signal C is supplied to a sound signal processing unit 40, andbased on the center channel sound signal C, the sound signal processingunit 40 produces a left sound signal for center channel positioning CL,and a right sound signal for center channel positioning CR, and suppliesthe sound signals CL and CR to the sound signal combining units 36, and38, respectively. A structure of the sound signal processing unit 40will be described later.

The left sound signal combining unit 36 combines the left sound signal Lwith the left sound signal for center channel positioning CL, andsupplies a left combined sound signal 102 through a DA conversion unit42, and an amplifier unit 44 to a left speaker 46 in the speaker unit14. Similarly, the right sound signal combining unit 38 combines theright sound signal R with the right sound signal for center channelpositioning CR, and supplies a right combined sound signal 104 through aDA conversion unit 48, and an amplifier unit 50 to aright speaker 52 inthe speaker unit 14.

In the AV amplifier device 12, a block denoted by reference numeral 54is composed of a processor such as a DSP, or a CPU which performs adigital process.

In a center channel positioning apparatus shown in FIG. 1, while thespeaker unit 14 includes the left speaker 46, and the right speaker 52,it does not include a center speaker. Therefore, a center channel soundsignal C from the decoder 16 is supplied to the sound signal processingunit 40, and based on the center channel sound signal C, the soundsignal processing unit 40 is arranged to produce a left sound signal forcenter channel positioning CL, and a right sound signal for centerchannel positioning CR, and distribute the sound signals CL, and CR tothe left speaker 46, and the right speaker 52, respectively.

Hereinafter, the sound signal processing unit 40 will be described.

In FIG. 2, a structure of the inside of a sound signal processing unitis shown.

In FIG. 2, the sound signal processing unit 40 produces a left soundsignal for center channel positioning CL, and a right sound signal forcenter channel positioning CR, based on a center channel sound signal C.The sound signal processing unit 40 includes an all-pass filter 56 atthe side of the right sound signal for center channel positioning CR.Here, the all-pass filter 56 is a filter whose amplitude characteristicfor a frequency characteristic is flat, and which shifts only a phase.The sound signal processing unit 40 has a structure mentioned above.Therefore, while a phase of the right sound signal for center channelpositioning CR is shifted, a phase of the left sound signal for centerchannel positioning CL is not shifted.

As mentioned above, by shifting a phase of the right sound signal forcenter channel positioning CR, sound based on a center channel soundsignal C is outputted from a left speaker 46, and a right speaker 52.

Although a phase of the right sound signal for center channelpositioning CR is shifted in the sound signal processing unit 40 shownin FIG. 2, it may be possible to shift a phase of the left sound signalfor center channel positioning CL.

As mentioned above, the sound signal processing unit 40 shifts a phaseof the right sound signal for center channel positioning CR, or a phaseof the left sound signal for center channel positioning CL. Here, thesound signal processing unit shifts a phase based on a processingcoefficient. The processing coefficient may be fixed or variable.Hereinafter, a case where the processing coefficient is variable will bedescribed.

The processing coefficient depends on an arrangement of a speaker, suchas a space between a left speaker and a right speaker, a distance from aspeaker to a listener. It is possible to change a processing coefficientbased on an arrangement of a speaker. An arrangement for such a changeis shown in FIG. 3.

In FIG. 3, an input of a sound signal processing unit is shown.

In FIG. 3, a memory unit 58 stores a plurality of different processingcoefficients, and a control unit 60 selects a proper processingcoefficient from the memory unit 58, and supplies it to the sound signalprocessing unit 40 in accordance with instructions from a user interface62. That is, when a user inputs information concerning an arrangement ofa speaker, to the user interface 62, the control unit 60 selects aproper processing coefficient for the arrangement of the speaker, fromthe memory unit 58, and supplies it to the sound signal processing unit40.

Now, in FIG. 4, the relationship in position between a listener, and aleft speaker and a right speaker is shown.

In an arrangement of speaker in FIG. 4, a space L1 between a leftspeaker 46 and a right speaker 52 is 1.5 m, and a center speaker 64 isshown by a broken line between both of the speakers 46 and 52. Althoughthe center speaker 64 is not actually arranged, it is virtually shownjust for the convenience of explanation. A distance L2 from a lineconnecting both of the speakers 46 and 52 to a listener 66 is 2 m.

In the case where the left speaker 46 and the right speaker 52 arearranged as shown in FIG. 4, an all-pass filter 56 in a sound signalprocessing unit 40 delays an input signal only around a band of 2 KHz byapproximately π (pi) radian (namely, a delay of approximately a half ofwavelength), and causes a delay of phase of input signal to be 0 radian(namely, no delay) at a band of low frequency, and around a band of 2KHz and more, as shown in FIG. 5.

As mentioned above, FIG. 5 shows an amount of delay of phase for eachband in an all-pass filter 56.

Hereinafter, a process of deriving an amount of delay of phase at eachband shown in FIG. 5 will be described.

In FIG. 6, a listener 66, and a left speaker 46 and a right speaker 52are arranged similarly with FIG. 4, and a subjective evaluationexperiment has been conducted.

In FIG. 6, a band noise generator 68 outputs a band noise signal 106 (awidth of band: ⅓ octave). The band noise signal 106 is supplied to aleft speaker 46 without a change of phase, and is supplied to a rightspeaker 52 after a delay of phase at a phase delay unit 57. In the casewhere an amount of delay of phase in an all-pass filter 56 is changed,it has been investigated in which direction a sound image 70 ispositioned relative to a listener 66. In FIG. 6, a direction of thesound image 70 is denoted by a degree of θ (theta). The result of theexperiment is shown in a graph of FIG. 7.

FIG. 7 shows how a center channel positioning is changed, namely, how adegree of a center channel positioning is changed, in the case where anamount of delay of phase is changed at each band. A bar-shaped indicator68 on the right side in FIG. 7 shows that an indication in each area ina graph of FIG. 7 corresponds to what degree of a center channelpositioning. For example, in an area 70 in a graph of FIG. 7, it isnoticed from the indicator 68 that a degree of a center channelpositioning is approximately 80 degree (namely, a sound image ispositioned approximately laterally).

In FIG. 7, in an area other than around an area of 2 KHz, since a degreeof phase is 0 radian, and a degree of a center channel positioning is 0degree (namely, positioned right in front), it is selected that a degreeof phase is made 0 radian in the area (namely, a phase is not delayed).

On the other hand, around an area of 2 KHz, there exist two phases whosedegree of a center channel positioning is 0 degree. That is, around anarea of 2 KHz, in two areas 72 (a degree of phase: π(pi) radian) and 74(a degree of phase: 0 radian) which are denoted by a broken line, adegree of center channel positioning is 0 degree. Therefore, it ispossible to select the two areas 72 (a degree of phase: π(pi) radian)and 74 (a degree of phase: 0 radian). However, the area 72 (a degree ofphase: π(pi) radian) is selected for the following reason.

First, FIG. 8 shows the difference in level between both ears, namely,shows the result of measure of the difference in level between both earsin the case where a dummy head microphone is located at a listeningposition.

A bar-shaped indicator 76 on the right side in FIG. 8 shows that anindication in each area in a graph of FIG. 8 corresponds to what degreeof the difference in level between both ears. For example, in an area 78in a graph of FIG. 8, it is noticed from the indicator 76 that thedifference in level between both ears is approximately 10 dB (a level ofsound pressure is big at a left ear), while in an area 80, it is noticedfrom the indicator 76 that the difference in level between both ears isapproximately −10 dB (a level of sound pressure is big at aright ear).

In FIG. 8, it is noticed that an area in which the difference in levelbetween both ears is 0 which is ideal is an area whose phase is around0, π(pi), or π(pi) radian.

Now, FIG. 9 shows the sum of power at both ears, namely, shows theresult of measure of the sum of power at both ear in the case where adummy head microphone is located at a listening position.

A bar-shaped indicator 82 on the right side in FIG. 9 shows that anindication in each area in a graph of FIG. 9 corresponds to what degreeof the sum of power at both ears. An maximum of the sum of power isnormalized to 0 dB. For example, in an area 84 in a graph of FIG. 9, itis noticed from the indicator 82 that the sum of power at both ears isapproximately −2 dB.

In FIG. 9, around an area of 250 Hz, it is noticed that when a phase isapproximately π(pi) radian, the sum of power at both ears is lowered(see an area 86). On the other hand, around an area of 2 KHz, it isnoticed that when a phase is approximately 0 radian and approximately2π(pi) radian, the sum of power at both ears is lowered (see an area 88and an area 90).

From graphs of FIG. 8 and FIG. 9 mentioned above, an ideal phase isselected for each band. That is, a phase is selected for each band insuch a way that the difference in level between both ears is maintainedaround 0 from a graph of a FIG. 8, and the sum of power at both ears isnot lowered from a graph of a FIG. 9. When such a selection is made, aconcept of degree of center positioning is used, and a degree of centerpositioning is defined by the following equation for evaluation.(a degree of center positioning)=(1/(an absolute value of the differencein level between both ears))*(the sum of power at both ears)*(the weightof phase)

The degree of center positioning is calculated for each band. When aphase is changed for each band, an absolute value of the difference inlevel between both ears, and the sum of power at both ears change. Atthis time, (1/(an absolute value of the difference in level between bothears), and (the sum of power at both ears) are set to be normalized insuch a way that they change between 0 and 1, respectively.

Further, the weight of phase is added, because it is desirable that achange of phase is as small as possible. That is, the weight of phase isset to change linearly with a phase in such a way that the weight ofphase is a value of 1 when a phase is 0 radian, and the weight of phaseis a value of 0 when a phase is 2π(pi) radian.

As mentioned above, since (1/(an absolute value of the difference inlevel between both ears)), (the sum of power at both ears), and (theweight of phase) change between 0 and 1, a degree of center positioningchanges between 0 and 1.

Now, FIG. 10 is a view of graph showing a degree of center positioning.

A bar-shaped indicator 82 on the right side in FIG. 10 shows that anindication in each area in a graph of FIG. 10 corresponds to what degreeof center positioning. For example, in an area 94 and an area 96 in agraph of FIG. 10, from the indicator 92, a degree of center positioningis approximately 1, and in an area 98 in a graph of FIG. 10, from theindicator 92, a degree of center positioning is approximately 0.5. Froma graph of FIG. 10, in order for a degree of center positioning toapproach as 1 as possible, π(pi) radian is selected as a phase at a bandof approximately 2 KHz, and 0(pi) radian is selected as a phase at aband other than approximately 2 KHz. A phase for each band thus selectedcorresponds to a graph of FIG. 5 mentioned above.

As one embodiment of the present invention, a center channel positioningapparatus is used only for a band of frequency of approximately 1 KHz toapproximately 4 KHz. Hereinafter, this embodiment will be describedhereinafter.

As mentioned in an column of “BACKGROUND ART” of this specification, ina frequency band of approximately 1 to approximately 4 kHz, a level offrequency characteristic in the case where a center channel sound signalis reproduced by left and right speakers becomes lower than a level offrequency characteristic in the case where the center channel soundsignal is actually reproduced by a center speaker, by approximately 10dB. Therefore, in the embodiment, a center channel positioning apparatusis used only for a band of frequency of approximately 1 KHz toapproximately 4 KHz. Consequently, strange feeling in sound quality isnot caused for a listener.

This embodiment has an advantageous effect that strange feeling in soundquality is not caused for a listener, because an arrangement is one inwhich a phase is changed, even if a center channel sound signal is heardat a position apart from an original listener position, as compared withan arrangement mentioned in Patent document No. 1 in which a gain israised, i.e., a frequency characteristic is changed.

The present invention is not limited to the foregoing embodiment. Theembodiment is illustrative. Anything having substantially the sameconfiguration and producing similar effects as the technical ideasdescribed in the scope of claims of the present invention is included inthe technical scope of the present invention.

1. A center channel positioning apparatus, comprising: a sound signaloutputting unit which outputs a left sound signal, a right sound signal,and a center channel sound signal, a sound signal processing unit whichproduces a left sound signal for center channel positioning, and a rightsound signal for center channel positioning, based on the center channelsound signal, a left sound signal combining unit which combines the leftsound signal with the left sound signal for center channel positioningto output a left combined sound signal to be supplied to a left speaker,and a right sound signal combining unit which combines the right soundsignal with the right sound signal for center channel positioning tooutput a right combined sound signal to be supplied to a right speaker,wherein the sound signal processing unit changes a phase of at least oneof the left sound signal for center channel positioning and the rightsound signal for center channel positioning, based on a processingcoefficient, and the processing coefficient is calculated based on thedifference in level between both ears in the case where the left soundsignal for center channel positioning and the right sound signal forcenter channel positioning are reproduced simultaneously, and the sum ofpower at both ears of the left sound signal for center channelpositioning and the right sound signal for center channel positioning.2. A center channel positioning apparatus according to claim 1, whereinthe processing coefficient is further calculated based on the weight ofphase, and the weight of phase indicates a change of phase of the leftsound signal for center channel positioning, or the right sound signalfor center channel positioning.
 3. A center channel positioningapparatus according to claim 1, wherein the sound signal processing unitis composed of an all-pass filter.
 4. A center channel positioningapparatus according to claim 1, further comprising a speaker unitincluding a left speaker and a right speaker, wherein the processingcoefficient is changed based on an arrangement of the left speaker andthe right speaker of the speaker unit.
 5. A center channel positioningapparatus according to claim 1, wherein the phase is changed only at aband of frequency of 1 KHz to 4KHz.